1. Field of the Invention
The invention relates in general to a signal receiver, and more particularly, to a signal receiver that is tolerant of high-voltage signals.
2. Description of the Related Art
Accompanied by the perpetual evolvement of integrated circuit manufacturing technologies, the operating voltage in the integrated circuits continues to decrease. In new-generation integrated circuits, it is a common occurrence that external signals from old-generation integrated circuits are received. The voltage of these external signals is likely higher than the operating voltage of the new-generation integrated circuits.
Take a double-data-rate three synchronous dynamic random access memory (DDR3 SDRAM) for example. The specified operating voltage of the DDR3 SDRAM is 1.5V, whereas the operating voltages of the DDR1 and DDR2 SDRAMs are 2.5V and 1.8V, respectively. In the latest DDR4, the operating voltage is reduced to even as low as 1.2V. That is to say, for example, a receiver that is simultaneously compliant with DDR2/3/4 needs to withstand and process input signals having an operating voltage range from 1.2V to 1.8V.
Apart from the considering the tolerance for high-voltage signals, the design of a DDR receiver also needs to take factors including the output voltage slew rate, power consumption, signal propagation delay and circuit hardware costs into account. A circuit design is regarded satisfactory only when the numerous factors above are optimized.